Lens surfacing apparatus and method

ABSTRACT

An apparatus and method for grinding and polishing ophthalmic lenses in which the abrading or polishing surface is moved through an orbit which in a reference plane describes substantially an ellipse. Simultaneously the lens is moved through an orbit which in the same plane describes substantially a circle. The reference plane is normal to the axis of rotation of the drive shaft which moves the lens in its circular orbit. The mechanism for orbiting the lens permits the lens surface to remain in close contact with the lap surface and in a predetermined aligned relation with respect to the lap surface throughout the surfacing operation. The lens is maintained close to the base curve of the lap, resulting in improved lens-lap fit which is highly desirable in the grinding or polishing of toric lenses. The orbital paths given to the lens and the lap are obtained through rotating and rolling action. Lenses of high quality are produced in substantially reduced operating times.

United States Patent n 1 Behnke LENS SURFACING APPARATUS AND METHOD [75] Inventor: Adolph Behnke, Tampa, Fla.

[73] Assignee: Textron lnc., Tampa, Fla.

[22] Filed: Nov. 23, 1973 [21] Appl. No.: 418,763

[52] US. Cl ..5l/ll9;5l/l24 L;5l/133; 51/284 [51] int. Cl t. B24b 13/02; B24b 1/00 [58] Field of Search 51/57, 58, 60, H9, lZO, 5l/l24 R, 124 L, 133, 284

[56] References Cited UNITED STATES PATENTS [324.559 9/l93l McCabe 5l/l33 X 2,l92,486 3/1940 Lockhart t t 5l/6O X 3,389,508 6/l968 Suddarth 51/60 Primary Examiner-Donald G. Kelly Assistant ExaminerNicholas P. Godici Attorney, Agent, or Firm-Gary A. Walpert [451 July 8,1975

[57] ABSTRACT An apparatus and method for grinding and polishing ophthalmic lenses in which the abrading or polishing surface is moved through an orbit which in a reference plane describes substantially an ellipse. Simultaneously the lens is moved through an orbit which in the same plane describes substantially a circle. The reference plane is normal to the axis of rotation of the drive shaft which moves the lens in its circular orbit. The mechanism for orbiting the lens permits the lens surface to remain in close contact with the lap surface and in a predetermined aligned relation with respect to the lap surface throughout the surfacing operation. The lens is maintained close to the base curve of the lap, resulting in improved lens-lap fit which is highly desirable in the grinding or polishing of toric lenses. The orbital paths given to the lens and the lap are obtained through rotating and rolling action. Lenses of high quality are produced in substantially reduced operating times.

26 Claims, 23 Drawing Figures LENS SURFACING APPARATUS AND METHOD BACKGROUND OF THE INVENTION This invention relates to an apparatus and method for surfacing lenses, and more particularly, to improve ments in the apparatus and method for grinding and polishing the surfaces of toric or cylindrical ophthalmic lenses.

In order to improve and hasten the finishing of ground and polished optical surfaces various mechanisms have been used to move the lens blank relative to an abrasive tool in a manner that will perform the grinding or polishing operation and yet prevent the formation of streaks or aberrations or other distortions in the surface of the lens.

In the manufacture of toric lenses the grinding and polishing operation presents difficulties because of the compound curvatures involved. In order to produce a lens in which both the spherical and cylindrical powers are accurate, it is essential that the finished lens surface have a curvature that matches the toric surface curva ture of the abrading tool or lap used to grind and polish the lens. This presents a problem because the lens will fit the lap only when the base curve of the lens, which defines the spherical element. coincides with the base curve of the lap at its apex or equator.

This may be visualized by reference to FIG. 14 of the attached drawings. A toric surface (a segment of which would be representative of the abrading tool or lap) is shown with its equator along line AA. At any point or 0 on the toric surface there are two principal radii of curvature. SS represents the base curve and CC represents the cross curve. The plane of the cross curve CC is at right angles to the equator AA and contains the axis of revolution YY. The equator AA is in the plane of the base curve SS. The radius of curvature for the curve CC is constant, i.e., it is the same at any point on the surface of the torus. Thus, the radius of curva ture for cylindrical curve CC through point 0 is equal to that for curve C C, through point 0,. However, the radius of curvature for the curve SS changes with the location of point 0 on the toric surface. Thus, the radius of curvature for base curve SS through point 0 is larger thanthat for the curve S 8, through point 0 When a lens, illustrated at L in FIG. 14, having a cross curve CC, which defines the cylindrical element of the lens, and a base curve SS, equal to the curve of equator AA, is positioned on the toric surface so that curve SS corresponds to the curve of equator AA, there is a perfect fit between the two surfaces. However, as the lens, illustrated at L in FIG. 14, is moved away from equator AA so that the base curve of the lens is positioned along curve 5,5, of the toric surface, the amount of surface contact between the lens and the lap will be reduced.

Attempts to grind or polish a toric lens by moving the lens back and forth relative to the lap solely along the equator AA of the toric surface while applying abrading material (emery or rouge) result in a close lap fit. However, these attempts at producing a toric lens have proved unsatisfactory because gross streaks and distortions result in the lens caused by the constantly repeat ing rubbing pattern.

Various attempts have been made to overcome this problem, but none has proven completely satisfactory. For example, in addition to moving the lens back and forth relative to the lap along the equator of the lap,

prior art machines have been employed which give the lens a simultaneous breakup" motion transverse to the equator, i.e., in the direction of the cross curve CC. This greatly reduces the streaks resulting from the simple back and forth motion, but results in other problems, Since the surface contact between the lens and the lap is reduced as the lens is moved away from the equator, portions of the lens do not grind or polish properly. To alleviate this problem the corner portions of the lap are usually trimmed. Alternatively, various operator techniques have been resorted to, such as adjusting the magnitude of the stroke, but this expedient requires a high degree of operator skill in order to produce a satisfactorily finished lens.

Another disadvantage with this type of operation is that it is slow and the machinery necessary to produce the compound motion is expensive to construct and maintain and is noisy in operation, utilizing complex mechanisms consisting of levers, ball cranks and slides. A further disadvantage with the combination back and forth-breakup motion approach is that it is used primarily in grinding or polishing a concave lens while using a convex lap or abrading surface. The production of convex lens surfaces by use of a concave lap is extremely slow and difficult on such machines.

Another approach that has been used in the production of toric lens surfaces is to impart a circular orbital motion to the lap and simultaneously move the lens back and forth in the direction of the SS curve with a constant stroke while introducing a periodic breakup in one of the motions. While processing times are somewhat improved by the use of this combination, the lenslap fit problems remain and a skilled operator is required to obtain even reasonably acceptable finished lenses. In addition, essentially the same complex mechanisms are required with commensurate high initial machine expense and maintenance costs. The operation is noisy.

The present invention overcomes these and other disadvantages as will be apparent from the following summary and description of the invention.

SUMMARY OF THE INVENTION In accordance with the invention, there is provided a unique mechanism in which a lap is moved slowly over a path or orbit which in a reference plane describes substantially an ellipse, and simultaneously a lens is moved at a relatively rapid rate in an orbit which in the same reference plane describes substantially a circle. The reference plane is a plane normal to the axis of a drive shaft used to move the lens in its circular orbit. The relative position of the base curve of the lens and the base curve of the lap is maintained. The lens does not rotate or spin about its own axis, but is held in a predetermined aligned relation with respect to the lap surface during the simultaneous orbiting of the lap and the lens. The base curve of the lens is maintained relatively close to the base curve or equator of the lap for a substantial portion of the surfacing operation. This results in close contact between the lens and lap surfaces which reduces the time required to grind and polish the lens.

In the present invention the lens and lap surfaces are in close contact with each other over a nonrepetitive path during a normal lens surfacing operation. This virtually eliminates zones" or streaks of aberration and produces lenses having accurate base and cross curves on the lens. In the present invention no breakup" mechanism is required.

In the preferred embodiment of the present invention the orbital paths given to the lens and lap are obtained through a rotating and rolling action, thus eliminating the necessity for complex mechanisms with the disadvantages usually associated therewith.

I have found that the lenses produced while following the principals of the present invention have surfaces that are essentially free from aberrations. In addition. these lenses are produced in a shorter period of time than when following previously known lens grinding and polishing techniques. The lenses produced with my invention do not require any special operator skills or techniques. Lap trimming is unnecessary.

Another advantage of my invention is that, in addition to producing negative or concave toric lens surfaces on convex laps. it is also possible to produce high quality plus, or convex toric lens surfaces while using a concave lap surface.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective of a machine of the instant invention, surfacing a pair of lenses.

FIG. 2 is an enlarged front elevation of FIG. 1 with parts broken away, showing mainly the frame and the arrangement of parts within it. The upper cover is shown in dotted lines and may be considered hinged in a back position. the various control parts being mounted on it, but not shown except for FIG. I.

FIG. 3 is a horizontal sectional view taken generally along line 33 of FIG. 2, showing mainly the upper motion mechanism.

FIG. 4 is another lower horizontal sectional view taken along line 4-4 of FIG. 2, showing the lower motion mechanism.

FIG. 5 is a vertical section through the machine generally along line 55 of FIG. 2. It shows both the upper and lower motion mechanisms in a complete side elevation.

FIG. 6 is a vertical section taken generally along line 66 of FIG. 4 with parts of the machine shown in dash line illustrating the tilting action of the lower motion mechanism relative to the machine frame.

FIG. 7 is a vertical sectional view taken generally along line 77 of FIG. 4 with parts of the machine removed for clarity. It shows part of the lower motion mechanism.

FIG. 8 is a vertical sectional view along line 88 of FIG. 3.

FIGS. 9 and I are vertical sections taken generally along lines 9-9 and IO-IO of FIG. 3, respectively.

FIG. I l is a front view of a modification of the device used to provide the tilting action of the lower motion mechanism.

FIG. 12 is a side elevation of FIG. 11.

FIG. 13 is a modification ofa tilt cam used in still another embodiment of the invention.

FIG. I4 is a diagram used to illustrate the spherical and cross curvatures of an abrading tool of the type re quired to grind and polish cylindrical or toric lenses.

FIG. I is a schematic representation of a lens-lap movement diagram of the type obtainable on one form of prior art lens surfacing machine.

FIG. 16 is a schematic representation of a lens-lap movement diagram of the typeobtained when using the preferred embodiment of the present invention.

FIG. 17 is a schematic representation of a modified lens-lap movement diagram of the type obtained when using a modified cam such as shown in FIG. 13.

FIG. 18 is a plan view of the path diagram of the lens movement.

FIG. I9 is a plan view of the path diagram of the lap movement.

FIGS. 20 and 21 are illustrations of projected images resulting from striations and aberrations in lenses lapped on prior art lens surfacing machines.

FIG. 22 is an illustration of the projected image of a lens ground and polished in accordance with the present invention and showing a complete lack of striations or aberrations.

FIG. 23 is a schematic representation of a ray diagram of the type produced in checking a lens for imperfections in accordance with known principles as described in US. Pat. No. 1,988,169. The pattern shown is typical of that produced when viewing imperfect lenses of the type illustrated in FIGS. 20 and 2].

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, FIG. I shows a pair of lenses being processed (ground or polished) simultaneously on a lens surfacing machine I4 embodying my invention. As best shown in FIGS. 2 and 5, each of the lenses l0 and I2 is held in a block 16 which, in turn, is held against rotation by a pair of block pins 18, 20 (FIG. 2) which project downwardly from pin holder 22 integral with and at the end of block holder arm, generally designated 24. The concave surface of each of the lenses is held against an abrading or polishing tool referred to as a lap 26, 28.

Laps 26 and 28, which may be referred to as the left and right-hand laps, respectively, when viewed from the front of the machine, are each held in lap support 32 which is integral with lap support arm 34 by spring biased lap clamp 30. Each of the laps 26 and 28, which may be made, for example, from cast iron, has convex surface with predetermined curvatures machined thereon. For example, base curvatures 36 is machined in one direction (FIG. 2) and cross curvatures 38 is machimed in a direction perpendicular to the plane of the base curve (FIG. 5). It will be recognized that base curvature 36 at the apex or equator of lap 26 corresponds to the base curve SS of the torus shown in FIG. 14, whereas cross curve 38 corresponds to cross curve CC or C1C1 Of 14.

An abrasive slurry is introduced between the surface of the lens and the surface of the lap by conventional means (not shown) and, as will be more fully described hereinafter, the lens and lap are moved relative to each other. The lens is moved in a circular orbit as shown in FIG. 18, and the lap is moved in an elliptical orbit as shown in FIG. 19. FIGS. 18 and 19 represent the orbital path that any point on the surface of the lens or lap, re spectively, will follow. As previously described, neither the lens or lap is permitted to rotate or spin" about its own axis. It should be noted that in following its elliptical orbit the lap moves not only in a side-to-side direc' tion. as shown by the double-headed arrow 40 in FIG. 2, but also moves toward and away from the panel face 42 of the surfacing machine, as shown by the doubleheaded arrow 44 of FIG. 6. Each lens I0, 12, through its associated lens block l6, 18, respectively, is held against lap 26, 28, respectively, by pins 18 and 20. The surface of the lens remains in contact with the surface of the lap throughout the grinding or polishing operation. The operation is continued until the lens surface conforms to the predetermined compound curvatures of the lap. It will be understood that each lap may be readily replaced with any one of a series of laps ma chined to the desired combination of base and cross curves. Lenses having a wide range of curvatures may be ground or polished on my surfacing machine.

Upper Machine Structure Referring now more specifically to the mechanism for imparting a circular orbit to each of the lenses, machine frame generally designated 46, which may be a metal casting, comprises back wall 48 and side walls 50 and 52, as well as upper cross shelf 54. Cross shelf 54 contains drive crank housing 56 and a pair of idler crank housings 58 and 60. Idler crank housings 58 and 60 are identical. Bracket 62 is fastened to cross shelf 54 by bolts 64, 66. Upper motion motor 68 is fastened to bracket 62 by bolts 70. Shaft 74 extends from motor 68 and sheave 76 is keyed thereto.

Sheave 76 is connected by belt 78 to sheave 80 keyed to drive shaft 82, which forms a part of drive crank mechanism, generally designated 88. Drive shaft 82 is journaled at its lower end in bearings 84 mounted within drive crank housing 56, as shown in FIG. 9. Flat circular member 86 is eccentrically mounted on drive shaft 82 and adapted to rotate therewith. Member 86 is mounted for free rotation, through bearing 90, in oscillating platform generally designated 94. Rotation of drive shaft 82 will cause oscillating platform 94 to move in a circular orbit about drive shaft 82. A counterweight 95 is fixedly attached to drive shaft 82 to assure smooth operation of the oscillating platform and associated parts.

As shown in FIG. 8, extending upwardly from oscillating platform 94 are three flanges 102, I04, I06 which support pivot shaft I08. Pivot shaft 108 is held against rotation within flanges 102, 104 and 106.

Oscillating platform 94 also contains two circular apertures 98 and 100, adapted to receive idler support crank mechanisms, generally designated I01 and 103, respectively. These two idler support crank mechanisms are identical. Their function, along with drive crank mechanism 88, is to provide a three-point support for oscillating platform 94 on the upper cross shelf 54 of machine frame 46. In addition, the two idler support crank mechanisms preserve alignment of the lens supporting structure and thus maintain alignment of the base curve of the lens with the base curve of the lap. Referring to FIG. 10, and describing the structure of only idler support crank mechanism 101, bearing 112 is mounted within aperture 98. Crank pin is mounted for rotation within bearing 112. One end of crank arm 114 is fastened to the lower end of crank pin 110. An idler shaft 116 is mounted for rotation within bearings 118 of idler crank housing 58. Idler support crank mechanisms 101 and 103 will support oscillating platform 94 as the latter moves in its circular orbit caused by rotation of drive shaft 82 within drive crank mechanism 88.

Each of a pair of generally A-shaped (FIG. 3) oscillating arms, generally designated I20, 122, is journaled in bearings 124 for rotation about pivot shaft 108 (see FIG. 8). The oscillating arms are mounted to prevent axial movement along pivot shaft 108. Each of the 0scillating arms is independently mounted on the pivot shaft. The two oscillating arms 120 and 122 are essentially alike, it being understood, of course, that they differ to the extent that arm 120 is the right oscillating arm and arm 122 is the left oscillating arm as viewed from the front of the surfacing machine as shown in FIG. I. Because of the substantial identity of the two oscillating arms, it will only be necessary to describe one and its relationship to the surfacing machine in order to give those skilled in the art a full understanding of the structure and operation of the arms.

Referring then to the right-hand oscillating arm 120 (the lower arm in FIG. 3), cross member I26 of the A- shaped arm has bearing I28 mounted therein. The head of the A-shaped arm contains bearing 132. Pin holder shaft I34, having its axis perpendicular to the axis of pivot shaft 108, is journaled for rotational movement within bearings I28 and I32 of oscillating arm 120. The inner end 136 of shaft 134 is secured within the oscillating arm in a conventional manner by a slotted hex nut 138.

The opposite end 140 of shaft 134 extends through an aperture in baffle 142 which covers a circular opening 144 in panel face 42. Baffle 142 is secured to the panel face by a plurality of cap screws I46 passing through a baffle ring 148, baffle 142 and into threaded apertures in panel face 42. Block holder arm 24 is secured to shaft 134 by clamp 150. As previously described, a pair of block pins 18, 20 extend downwardly from pin holder 22 which is integral with block holder arm 24. The axes of these pins are aligned and are in a plane parallel to the axis of pivot shaft I08. The lower end of each of the pins 18, 20 is shaped, such as by rounding, to fit into a corresponding socket in lens block I6 in a manner well known to those skilled in the art. The rounded ends of each of the pins 18, 20 permits pivotal movement of the lens block with respect to the pins about an axis parallel to the axis of pivot shaft 108.

Referring to FIG. 2, bracket 152 is secured to side wall 50 of machine frame 46. An air cylinder and piston means 154 is resiliently held in the upper end of bracket 152 by resilient rings 156, I58 and a knurled nut I60 threadedly secured to a stem 162 that extends upwardly from the top of the air cylinder. Piston rod 164 extends downwardly from air cylinder and piston 154. An air cylinder adapter 166 is fastened to the lower end of rod 164 by jam nut 168. A pressure pin 170 having a rounded end 172 is disposed at the lower end of the air cylinder adapter. A corresponding socket 174 in the web 176 of A-shaped oscillating arm 120 (see FIG. 3) is adapted to receive the rounded end 172 of pressure pin 170. A predetermined downward pressure may be exerted against oscillating arm 120 by applying air pressure in a conventional manner to air cylinder and piston means I54. Pressure applied to arm 120 will be transmitted through head 130, pin holder shaft 134, block holder arm 24, pins 18, 20 and block 16 to lens 12 in contact with lap 28.

It will be understood that a second, identical air cylinder and piston means 178 mounted on bracket 180 may be utilized to exert a pressure on the left-hand A- shaped oscillating arm 122, independently of that applied to arm 120. Pressure applied to arm 122 will, of course, be transmitted to lens 10 in contact with lap 26. While I have described cylinder and piston means 154 and 178 as being operated by air, otlif fluids, such as hydraulic fluid, may be used to exert the Bledetermined :lownward pressure on arms 120 and 122. Mechanical means, such as a spring member, could also be used for this purpose.

The Motion Imparted to the Lens Actuation of motor 68 by a conventional swtich mounted on cabinet cover 182 will cause rotation of shaft 74 and sheave 76. Sheave 80, driven by belt 78, causes drive shaft 82 to rotate. A circular orbital motion is transmitted to oscillating platform 94 through eccentrically mounted drive crank mechanism 88. This motion is in turn transmitted through pivot shaft 108 held in platform 94 to each of the two A-shaped oscillating arms 120, 122 and thence to pin holder shaft 134, block holder arm 24, block pin 18, 20, block 16 and lenses 10, 12.

When I state that the orbital motion imparted to the lens is circular, I mean that when the lens is orbited, any point on the lens surface will describe a circle when viewed. for example, in the plane of the paper as shown in FIG. 3. This plane is normal or perpendicular to the axis of rotation of drive shaft 82, which as described moves the lens, through drive crank mechanism 88, in its circular orbit.

In addition to the circular orbital motion imparted to each of the A-shaped oscillating arms 120, 122, each of these arms is free to pivot, independently of the other, about pivot shaft 108, through bearings 124. Thus, as the lens moves inwardly and outwardly in its circular orbit with respect to the panel face of the sur facing machine (see FIG. it also is free to follow the cross curvature 38 of the lap 28 by virtue of the combined pivotal action of arm 120 about shaft 108 and the pivotal movement of the lens block 16 against the rounded end of aligned pins 18, 20, the latter movement being parallel to the axis of shaft 108.

As the lens moves laterally in its circular orbit with respect to the face of the surfacing machine, it is free to follow the base curvature of the lap by virtue of the free rotational movement of pin holder shaft 134 in bearings 128, 132 in the cross member 126 and head 130, respectively, of oscillating arm 120.

The radius of the circular orbit in which the lenses 10, 12 will travel is, of course, controlled by the extent of the eccentricity of flat circular member 86 with respect to drive shaft 82 in drive crank mechanism 88. I have found that for lenses having a diameter of between about 50 and 72 mm, a radius of three hundred thousandths of an inch (0.300 inch for this orbit produces exceptionally good grinding and polishing results. The speed with which the lens is driven about its circular orbit may be controlled by use of a variable speed motor 68 or by changing the diameter of sheave 76 or sheave 80. For optimum results, the lens should be moved relatively rapidly in a circular path, in comparison with the speed of the lap which, as will be described hereinafter, is simultaneously driven about an elliptical path. I have found that for about 95% of required spherical and cylindrical powers a circular orbiting speed of between about 850 and 900 revolutions per minute produces good quality grinding and polishing results in minimum operating time. When using extremely high curvatures. especially when grinding or polishing the convex surface of a lens, lower lens orbiting speeds should be used.

Lower Machine Structure Referring to FIGS. 2, 4, 5 and 7, and to the mechanism for imparting an elliptical orbit to the lap, lower cross shelf 184 is attached to side walls 50, 52 of machine frame 46 by bolts 186, 188, respectively. Shaft supporting members 190, 192 extend upwardly from shelf 184. Pivot shaft 194 is fixedly mounted within supporting members 190, 192. The front end 196 of tilt frame, generally designated 198, is mounted for pivotal movement about pivot shaft 194 through bearings 200 disposed a short distance inwardly from the opposite ends of shaft 194. A lower motor 202 and speed reducer 204 are secured by bolts 206 to the opposite or rear end 208 of tilt frame 198. A spring hook 236 is secured to the right end of the housing of motor 202. The upper end of pull down spring 238 is attached to spring hook 236 and the lower end of the spring is attached to spring post 240 mounted in the back wall 48 of machine frame 46.

Intermediate the front and rear ends of tilt frame 198, and integral therewith, is right-hand cam lever shaft support 210 (see FIG. 5). Cam lever shaft 212 is mounted for rotation within support 210 in front and rear bearings 214, 216, respectively. Shaft 212 is reduced in diameter in that portion of the shaft that extends through bearings 214, 216. The axis of rotation of cam lever shaft 212 is perpendicular to and in spaced relation from the axis of rotation of pi ot shaft 194.

The rear end of cam lever shaft 212 is threaded to receive nut 218. The shoulder of the shaft at its reduced portion contacts front bearing 214 and, together with the nut 218 on the rear end of shaft 212, prevents slippage of the shaft in support 210.

An annular baffle 220 is secured to cam lever shaft 212 intermediate front bearing 214 and the front end of the shaft 212. Lap support arm 34 is attached to the front end of shaft 212 by clamp 222 and bolts 224. Lap support 32, integral with lap support arm 34, mounts lap member 28 which is held firmly in place thereon by spring biased lap clamp 30. If desired, a conventional lap pilot member (not shown) may be used to position and further secure the lap to the lap support.

A second or left-hand cam lever shaft support 226 is also disposed on tilt frame 198 (FIG. 4). Support 226 carries a cam lever shaft 228 which is mounted for rotation in the support through from and rear bearings identical to bearings 214, 216. Left-hand lap support arm 34 is attached to the front end of shaft 228. It will be understood that both right and left-hand lap support arms, lap supports and lap clamp mechanisms are identical. The base and cross curvatures 36, 38, respectively, of one lap mounted in the apparatus may or may not be the same as those of the other lap mounted in the apparatus. The particular lap selected will depend on the spherical and cylindrical powers, i.e., the prescription to which the lens presented to the lap is to be ground or polished.

Extending forwardly from speed reducer 204 is drive shaft 230. Large circular cam 232 is keyed at 234 to shaft 230. As best shown in FIG. 7, the center 280 of cam 232 is offset with respect to the axis 282 of shaft 230.

Eccentrically mounted large cam 232 rides on cam roller 242 mounted for rotation on short shaft 284 extending from support 286 on lower cross shelf 184. The

outer roller-contacting surface of cam 232 is slightly crowned.

Again referring to FIG. 7, small circular cam 244 is fixedly mounted for rotation on shaft 230. If desired, small cam 244 may, as shown, be secured to the front face of cam 232 as by bolts 246. The center 288 of cam 244 is eccentrically mounted with respect to both the axis 282 of shaft 230 and the center 280 of large cam 232.

One end of right-hand cam lever 248 is keyed at 250 to the reduced section of cam lever shaft 212 between bearings 214 and 216. Cam lever 248 is secured to the shaft 212 by clamp 252 held by cap screws 254. A cam follower 256 is rotatably mounted at the opposite end of cam lever 248.

Similarly, one end of a second or left-hand cam lever 258 is keyed to cam lever shaft 228 and attached thereto by identical clamping means. Cam follower 260 is rotatably mounted on the opposite end of cam lever 258. Cam followers 256 and 260 ride on the peripheral surface of small circular cam 244. As shown in FIG. 2, cam biasing spring 262 connects left-hand cam lever 258 to right-hand cam lever 248 and assures that cam followers 256 and 260 will remain in contact with cam 244 during operation of the machine. The spring tension between the two cam levers may be adjusted by rotation of nut 264 on spring tension screw 266.

While I have shown independent motor 202 and speed reducer 204 as the means for driving shaft 230, it will be understood that shaft 230 could be driven from the same power source as that used to drive shaft 74 in the upper machine structure.

The Motion Imparted to the Lap Referring to FIGS. and 6, as drive shaft 230 rotates causing eccentrically mounted large cam 232 to rotate against cam roller 242, the tilt frame 198 will pivot about shaft 194 at the front end of the surfacing ma chine. Pull down spring 238 will cause the outer rollercontacting surface of cam 232 to remain in contact with cam roller 242. The pivotal movement of tilt frame 198 (together with the components mounted thereon) is illustrated by the dash line positioning in FIG. 6. Double-headed arrow 44 represents the manner in which the two lap holder arms 34 and the laps 26 or 28 mounted thereon oscillate toward and away from panel face 42 of the surfacing machine as tilt frame I98 pivots back and forth about shaft 194.

As will be described more fully hereinafter, this oscillation of the lap constitutes one component of motion of the lap during operation of the machine. The amplitude through which tilt frame 198 oscillates in its pivotal movement about the axis of pivot shaft 194 establishes the minor axis of the elliptical orbit described by a point on the lap surface.

Contact between the peripheral surface of small cam 244 and cam followers 256 and 260 is maintained by biasing spring 262 (see FIG. 2; the spring having been removed for clarity in FIG. 7). As shaft 230 is rotated. contact between cam follower 256 and eccentrically mounted small cam 244 will cause cam lever shaft 212 to oscillate about its axis as indicated by double-headed arrow 268. Similarly, cam lever shaft 228 will oscillate an equal amount about its axis as indicated by doubleheaded arrow 270. The oscillating motion of cam lever shaft 228 will be transmitted to left-hand lap holder arm 34 which will oscillate from side-to-side as shown by double-headed arrow 40 in FIG. 2. Oscillation of the left-hand lap holder arm 34 will, of course. be transmitted to the lap 26. The amplitude through which cam lever shaft 228 oscillates in its pivotal movement about its axis establishes the major axis of the elliptical orbit described by a point on the lap surface. Similarly, oscillation of cam lever shaft 212 results in oscillation of right-hand lap holder arm 34 and lap 28 affixed thereto.

Combined oscillation of the lap in the front-to-rear direction and in the side-to-side direction defines substantially an elliptical orbit. Thus, in referring to FIG. 3, a point on lap surface 26 or 28, when viewed in the plane of the paper, will describe substantially an ellipse when the lap is orbited. It will be recognized that this plane is normal or perpendicular to the axis of rotation of drive shaft 82, referred to above in connection with the upper machine structure. As stated above, I have found that an elliptical orbit with the major axis of the ellipse disposed in the direction of the base curvature of the lap results in excellent grinding and polishing results.

It will be understood that for each complete rotation of large cam 232 the tilt frame 198 will pivotally move about the axis of pivot shaft 194 through an amplitude that establishes the minor axis of the elliptical orbit of the lap. For each complete rotation of large cam 232, each cam lever shaft 212 and 228 will pivotally move about its axis through an amplitude that will establish the major axis of the elliptical orbit of the lap.

As shown in FIG. 19, the path which a point on the lap surface follows will define an elliptical or elongated, cigar-shaped orbit with the major axis of the ellipse in the direction of the base curvature of the lap. The major axis of the elliptical orbit in which the lap will travel is controlled by the amplitude of the oscillation of cam lever shafts 212 and 228 which, in turn, is controlled by the amount of offset of the center 288 of small cam 244 from the axis 282 of drive shaft 230. The minor axis of the elliptical orbit is controlled by the amplitude of the oscillation of tilt frame 198 about the axis of pivot shaft 194 which, in turn, is controlled by the amount of offset of the center 280 of large cam 232 from the axis 282 of the drive shaft 230. I have found that for lenses having a diameter of between about 50 and 72 mm. an ellipse having a major axis of 1.062 inch and a minor axis of 0.375 inch produces exceptionally good grinding and polishing results. The major axis of the elliptical orbit should be at least twice the minor axis of the elliptical orbit.

The speed with which the lap is driven about its elliptical orbit may, of course, be controlled by speed reducer 204. The lap should be moved relatively slowly as compared with the orbital speed of the lens which, as described above, is simultaneously being orbited in a circular path. I have found that a lap speed of between about and elliptical orbits per minute produces a satisfactory surface.

FIG. 16 is a schematic representation of the com bined lens-lap movement that results when a lens is moved in a circular orbit while simultaneously moving a lap in an elliptical orbit with the major axis of the ellipse in the direction of the base curvature of the lap. Line 272 represents the path that a point at the center of a lens which is orbiting rapidly in a circular path will follow relative to a lap during one relatively slow elliptical orbit of the lap. The dash line 273 in FIG. 16 represents the approximate total envelope that the center point of a lens will describe during a complete grinding or polishing operation comprising many elliptical orbits. During an actual grinding or polishing operation the lap will, of course, make a large number of elliptical orbits and the path that a point on a lens being ground or polished will follow relative to the lap surface will be far more complex than that shown in FIG. 16. Because the lap travels in an elliptical orbit and the lens in a circular orbit at the speeds heretofore described. the path that a point on a lens will follow during a grinding or polishing operation will not repeat. This greatly reduces one of the major causes of the formation of streaks or aberrations in the lens surface.

Moving the lens in a circular orbital path while simultaneously moving the lap in an elliptical path as described results in keeping the lens close to the spherical axis of the lap during a substantial portion of the grinding or polishing operation. As previously described, in grinding or polishing a toric lens it is desirable to keep to a minimum the distance that the lens is moved away from the apex or equator of the lap. The greater the separation. the greater the deviation in lens-lap fit. Conversely, the more closely the lens is kept to the base curve or equator AA of the lap, the better the fit between the lens and the lap. In surfacing a lens, maxi mum stock removal occurs when there is maximum lens-lap contactv Thus. the closer the lens is kept to the base curve of the lap, the greater the efficiency of the surfacing operation and the shorter the time required to grind or polish the lens surface.

FIG. 15 is a schematic representation of the com bined lens-lap movement that results in using a prior art surfacing machine. Line 274 represents the path that a point at the center of a lens will follow where the lap is moved in a circular orbit and the lens is oscillated from side-to-side in the direction of double-headed arrow 276 and at the same time is given a slight breakup motion in a direction transverse thereto as indicated by the direction of double-headed arrow 278. Dash line 275 in FIG. 15 represents the approximate total envelope that the center point ofa lens will describe with this combination of motions. In FIG. 15 the lens deviates from the equator AA of the lap through a greater portion of its travel than the lens shown in FIG. 16, thus resulting in a poor lens-lap fit through most of the travel of the lens relative to the lap.

An operation in which the path of a point on the lens follows that shown in line 274 of FIG. 15 has two disadvantages. The first is that the path of the lens over the surface of the lap may be repeated frequently during a normal surfacing operation resulting in aberrations or streaks on the lens surface. The second is that the reduced lens-lap fit requires a longer grinding or polishing time.

A comparison of the paths in FIGS. 15 and 16 shows that in FIG. I6 the center of the lens is near the base curve of the lap during a far greater portion of the travel of the lens relative to the lap than in the case of the path shown in FIG. 15. It will be noted that in FIG. 15 the center of the lens is in close proximity to the base curve of the lap only where the lens is moving across the base curve of the lap.

Table I shows a comparison of the time required for grinding and polishing the surfaces of identical toric lens blank using the prior art type of lens-lap motion illustrated in FIG. 15 and using the lens-lap motion of my invention with its improved lens-lap fit as illustrated in FIG. 16. In each case the same lap was used and other operating conditions were maintained the same.

Lap: ellipitical orbit (see FIG. 16)

FIGS. 20 and 2] illustrate typical shadow scope patterns created by distortions found in lenses ground or polished on known surfacing machines, whereas a lens ground and polished in accordance with the present invention will produce a clear image as illustrated in FIG. 22. No discernible streaks or aberrations, such as those represented by dotted lines 291 in FIGS. 20 and 2], are visible in FIG. 22. The manner in which lenses may be tested for optical quality using the shadow scope tech nique is schematically shown in FIG. 23, and more fully described in US. Pat. to Duckwall No. l,988.l69. A pinpoint of light 290 is projected through a lens 292 to a ground glass or translucent screen 294. The rays of light indicated at 296 will be effected by any irregular ity in the lens surface. This will cause a variation of in tensity of the light as it strikes screen 294. While it should be understood that this means for inspecting lenses forms no part of my invention, it is a useful tool in observing the superior results obtained when grinding and polishing lenses according to my invention as compared to the results obtained when using surfacing machines heretofore available.

A modified form of tilt cam that may be used with my invention is shown in FIG. 13. A nomcircular, generally elliptically-shaped cam 298 may be used in place of large circular cam 232 in order to control the movement of lap members 26 and 28. Replacing large circu lar cam 232 on shaft 230 with elliptically-shaped cam 298 will cause the laps to travel in what I refer to as a collapsed elliptical path. Referring to FIG. 17, line 300 represents the path that a point at the center of a lens which is orbiting rapidly in a circular path will follow relative to a lap during several relatively slow collapsed elliptical orbits of the lap. Dash line 301 in FIG. 17 represents the approximate total envelope that the center point of a lens will describe using this combination of motions. As shown in FIG. 17, the center of the lens remains relatively close to the base curve of the lap during the surfacing operation, thus maintaining a good lens-lap fit as previously described. In FIG. 17 the deviation of the center of the lens from the base curve of the lap for a substantial portion of the path is even less than that shown in FIG. 16. It will be understood that the precise shape of the orbit that the lap will follow may be varied by changing the shape of the tilt cam, bearing in mind that a generally elliptical orbit that is very elongated in the base curve direction of the lap is desirable.

A modification in the mechanism used to tilt the tilt frame 198 about pivot shaft 194 is shown in FIGS. 11 and 12. Support 286 extending upwardly from lower cross shelf 184 holds ball 302. Universal socket 304 which forms a part of hinge member 306 is mounted for free universal movement about the ball. A bore 308 extends through hinge member 306, and the outer ends 312 and 314 of pin 310 mounted within bore 308, extend into ears 316 and 318, respectively, of block 315. Block 315 is pivotally movable relative to hinge member 306, which in turn is movable relative to ball 302.

Flat circular member 324 is eccentrically mounted on shaft 230 and is adapted to rotate therewith. the center point 326 of member 324 is offset from the axis 282 of shaft 230. Circular member 324 is mounted for rotation within bearing 320 positioned within block 315. Circular cam 319 is also mounted eccentrically with respect to the axis 282 of shaft 230 and is adapted to rotate therewith. The center point 322 of cam 319 is offset with respect to both the axis 282 of shaft 230 and the center 326 of member 324. Circular cam 319 may be integral with flat circular member 324, as shown in FIG. 12, or may be separately mounted on shaft 230.

It will be understood that the mechanism shown in FIGS. 11 and 12 is used in place of the large cam 232 and small cam 244 previously described. Rotation of shaft 230 will cause eccentrically mounted member 324 to rotate within block 315. This in turn will cause block 315 to pivot about shaft 310, and hinge member 306 to pivot on ball 302, thus resulting in a tilting of frame 198 about shaft 194 (FIG. 6) in the same manner as previously described. This tilting movement will be transmitted to the lap holder arms 34 and together with the oscillation of the cam lever shafts 212 and 228, caused by contact of cam followers 256 and 260 with the surface of cam 319 in place of cam 244, as previously described, will cause the laps to orbit in an elliptical path.

The terms and expressions which have been employed here are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. A lens grinding machine for forming a compound curvature on a lens surface comprising a lap having a compound curvature on the surface thereof,

means for moving said lap in a first orbit which in a reference plane describes substantially an ellipse,

a lens carrying block,

means for moving said block, simultaneously with the orbital movement of said lap, in a second orbit which in said reference plane describes substantially a circle,

said means for moving said block comprising a first drive shaft having a first axis of rotation and said reference plane being a plane normal to said first axis of rotation,

and means for maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relation with respect to said lap surface during the simultaneous orbiting of said lap and said block.

2. A lens grinding machine as recited in claim 1 wherein the means for moving said block are independent of the means for moving said lap.

3. A lens grinding machine as recited in claim 1 wherein said means for moving said lap in said first orbit comprise a machine frame,

a tilt frame mounted for pivotal movement about a second axis within said machine frame,

a first cam lever shaft mounted in said tilt frame,

a lap support mounted on said first cam lever shaft,

means for pivotally moving said tilt frame about said second axis through a first predetermined amplitude to establish the minor axis of said first orbit,

said first cam lever shaft being mounted for pivotal movement relative to said tilt frame about a third axis perpendicular to and in spaced relation from 15 said second axis,

and means for pivotally moving said first cam lever shaft about said third axis through a second predetermined amplitude to establish the major axis of said first orbit.

4. A lens grinding machine as recited in claim 3 wherein said means for pivotally moving said tilt frame about said second axis comprise a second drive shaft,

means mounted on said tilt frame for rotating said second drive shaft,

a first cam eccentrically mounted on said second drive shaft and adapted to rotate with said second drive shaft,

and a cam roller mounted for rotation in said machine frame,

said first cam being adapted to contact said cam roller whereby on rotation of said second drive shaft said tilt frame is pivotally moved about said second axis through said first predetermined amplitude with each complete rotation of said first cam.

5. A lens grinding machine as recited in claim 4 wherein said first cam is circular.

6. A lens grinding machine as recited in claim 4 wherein said first cam is non-circular.

7. A lens grinding machine are recited in claim 4 wherein said first cam is elliptical.

8. A lens grinding machine as recited in claim 4 wherein said means for pivotally moving said first cam lever shaft about said third axis comprise a second cam, said second cam being eccentrically mounted on said second drive shaft,

a first cam lever mounted on said first cam lever shaft and being adapted to rotate with said first cam lever shaft,

a first cam follower mounted on said first cam lever and adapted to rotate against said second cam, whereby on rotation of said second drive shaft said first cam lever shaft is pivotally moved about said 55 third axis through said second predetermined amplitude with each complete rotation of said first cam.

9. A lens grinding machine as recited in claim 1 wherein said means for moving said block in said second orbit further comprise a machine frame,

said first drive shaft supported in said frame,

means for rotating said first drive shaft about said first axis of rotation,

an oscillating platform eccentrically mounted on said first drive shaft being adapted to move in a circular orbit on rotation of said first drive shaft,

means to support said oscillating platform for oscillating motion in said machine frame,

a pivot shaft rigidly mounted in said oscillating platform and means connecting said pivot shaft to said lens carrying block.

10. A lens grinding machine as recited in claim 9 wherein said means for maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relation with respect to said lap surface during the simultaneous orbiting of said lap and said block comprise an arm mounted for pivotal movement with respect to said oscillating platform along a second axis,

a pin holder shaft mounted for pivotal movement relative to said arm about a third axis perpendicular to and spaced from said second axis,

a block holder arm mounted on said pin holder shaft,

a pin holder integral with said block holder arm,

a pair of block holder pins extending downwardly from said pin holder,

said lens carrying block being adapted to receive said pair of block holder pins and to permit pivotal movement of said block with respect to said pins about an axis parallel to said second axis,

and means for exerting a predetermined downward pressure on said arm.

ll. A lens grinding machine as recited in claim 3 wherein the major axis of said first orbit is at least twice the minor axis of said first orbit.

12. A lens grinding machine as described in claim 4 further comprising a second cam lever shaft mounted in said tilt frame,

a second lap support mounted on said second cam lever shaft, said second cam lever shaft being mounted for pivotal movement relative to said tilt frame about a fourth axis parallel to said third axis,

said means for pivotally moving said first cam lever shaft about said third axis further comprising means to simultaneously pivotally move said second cam lever shaft about said fourth axis through said second predetermined amplitude.

13. A lens grinding machine as recited in claim 12 wherein said means for pivotally moving said first and second cam lever shafts about said third and fourth axes, respectively, further comprise a second cam, said second cam being eccentrically mounted on said second drive shaft,

a first cam lever mounted on said first cam lever shaft and being adapted to rotate with said first cam lever shaft,

a first cam follower mounted on said first cam lever,

a second cam lever mounted on said second cam lever shaft and being adapted to rotate with said second cam lever shaft,

a second cam follower mounted on said second cam lever.

means for maintaining said first and second cam followers in contact with said second cam,

whereby on rotation of said second drive shaft each of said first and second cam lever shafts is pivotally moved about its corresponding third and fourth axes, respectively, through said second predetermined amplitude with each complete rotation of said first cam.

14. A lens grinding machine as recited in claim 13 wherein said means for maintaining said first and second cam followers in contact with said second cam comprise a tension spring connecting said cam levers.

15. A lens grinding machine as recited in claim 14 further comprising means to adjust the tension in said spring.

16. A lens grinding machine as recited in claim 1 further comprising a second lens carrying block and wherein said means for moving said block in said second orbit simultaneously with the orbital movement of said lap further comprise means to simultaneously move said second block in a third orbit substantially identical to said second orbit.

17. A lens grinding machine as recited in claim 16 further comprising a machine frame,

said first drive shaft supported in said frame,

means for rotating said first drive shaft about said first axis of rotation,

an oscillating member eccentrically mounted on said first drive shaft being adapted to move in a fourth orbit substantially identical to said second and third orbits on rotation of said first drive shaft,

means to support said oscillating member for oscillating motion in said machine frame,

a pivot shaft rigidly mounted in said oscillating member,

means connecting said pivot shaft to said lens carrying block,

and independent means connecting said pivot shaft to said second lens carrying block.

18. A lens grinding machine as recited in claim 9 wherein said means to support said oscillating member for oscillating motion in said machine frame comprise a pair of idler cranks mounted in said machine frame.

19. A lens grinding machine as recited in claim 10 wherein said means for exerting a predetermined downward pressure on said arm comprise a cylinder and piston means mounted on said machine frame, a pressure pin integral with said piston means, a socket in said arm to receive said pressure pin, and means to supply fluid under pressure to said cylinder and piston means.

20. A lens grinding machine as recited in claim 3 wherein said means for pivotally moving said tilt frame about said second axis comprise a second drive shaft,

means mounted on said tilt frame for rotating said second drive shaft,

a circular member eccentrically mounted on said second drive shaft and being adapted to rotate with said drive shaft,

a block,

said circular member being mounted for rotation with respect to said block, and

hinge means connecting said block to said machine frame whereby on rotation of said second drive shaft said tilt frame is pivotally moved about said second axis through said first predetermined amplitude with each complete rotation of said second drive shaft.

21. A lens grinding machine as recited in claim 20 wherein said means for pivotally moving said first cam lever shaft about said third axis comprise a first cam lever mounted on said first cam lever shaft and being adapted to rotate with said first cam lever shaft,

a cam eccentrically mounted on said second drive shaft and being adapted to rotate with said second drive shaft, and

a cam follower mounted on said first cam lever and adapted to rotate against said cam, whereby on ro tation of said second drive shaft said first cam lever shaft is pivotally moved about said third axis through said second predetermined amplitude with each complete rotation of said second drive shaft.

22. The method of forming a compound curvature on a lens surface comprising moving a lap having a compound curvature on the surface thereof in a first orbit which in a reference plane describes substantially an ellipse,

simultaneously moving a lens carrying block in a second orbit which in said reference plane describes substantially a circle,

said reference plane being a plane normal to the axis of rotation of said circular orbit,

and maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relation with respect to said lap surface during the said orbiting of said lap and said block.

23. The method as recited in claim 22 wherein said lap is moved in said first orbit at between about US and I25 orbits per minute and said block is moved in said second orbit at between about 850 and 900 orbits per minute.

24. The method as recited in claim 22 wherein the major axis of said second orbit is at least twice the length of the minor axis of said second orbit.

25. A lens grinding machine for forming a compound curvature on a lens surface comprising a lap having a compound curvature on the surface thereof,

means for moving said lap in a first orbit,

a lens carrying block,

means for moving said block, simultaneously with the orbital movement of said lap, in a second orbit,

wherein one of said lap and said block moves in an orbit which in a reference plane describes substantially a circle and the other of said lap and said block moves in an orbit which in said reference plane describes substantially an ellipse, and

means for maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relationship with respect to said lap surface during the simultaneous orbiting of said lap and said block.

26. The method of forming a compound curvature on lens surface comprising moving a lap having a compound curvature on the surface thereof in a first orbit,

simultaneously moving a lens carrying block in a second orbit,

wherein one of said lap and said block moves in an orbit which in a reference plane describes substantially an ellipse. the other of said lap and said block moves in an orbit which in said reference plane describes substantially a circle, said reference plane being a plane normal to the axis of rotation of said circular orbit, and

maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relationship with respect to said lap surface during said orbiting of said lap and said block. 

1. A lens grinding machine for forming a compound curvature on a lens surface comprising a lap having a compound curvature on the surface thereof, means for moving said lap in a first orbit which in a reference plane describes substantially an ellipse, a lens carrying block, means for moving said block, simultaneously with the orbital movement of said lap, in a second orbit which in said reference plane describes substantially a circle, said means for moving said block comprising a first drive shaft having a first axis of rotation and said reference plane being a plane normal to said first axis of rotation, and means for maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relation with respect to said lap surface during the simultaneous orbiting of said lap and said block.
 2. A lens grinding machine as recited in claim 1 wherein the means for moving said block are independent of the means for moving said lap.
 3. A lens grinding machine as recited in claim 1 wherein said means for moving said lap in said first orbit comprise a machine frame, a tilt frame mounted for pivotal movement about a second axis within said machine frame, a first cam lever shaft mounted in said tilt frame, a lap support mounted on said first cam lever shaft, means for pivotally moving said tilt frame about said second axis through a first predetermined amplitude to establish the minor axis of said first orbit, said first cam lever shaft being mounted for pivotal movement relative to said tilt frame about a third axis perpendicular to and in spaced relation from said second axis, and means for pivotally moving said first cam lever shaft about said third axis through a second predetermined amplitude to establish the major axis of said first orbit.
 4. A lens grinding machine as recited in claim 3 wherein said means for pivotally moving said tilt frame about said second axis comprise a second drive shaft, means mounted on said tilt frame for rotating said second drive shaft, a first cam eccentrically mounted on said second drive shaft and adapted to rotate with said second drive shaft, and a cam roller mounted for rotation in said machine frame, said first cam being adapted to contact said cam roller whereby on rotation of said second drive shaft said tilt frame is pivotally moved about said second axis through said first predetermined amplitude with each complete rotation of said first cam.
 5. A lens grinding machine as recited in claim 4 wherein said first cam is circular.
 6. A lens grinding machine as recited in claim 4 wherein said first cam is non-circular.
 7. A lens grinding machine are recited in claim 4 wherein said first cam is elliptical.
 8. A lens grinding machine as recited in claim 4 wherein said means for pivotally moving said first cam lever shaft about said third axis comprise a second cam, said second cam being eccentrically mounted on saId second drive shaft, a first cam lever mounted on said first cam lever shaft and being adapted to rotate with said first cam lever shaft, a first cam follower mounted on said first cam lever and adapted to rotate against said second cam, whereby on rotation of said second drive shaft said first cam lever shaft is pivotally moved about said third axis through said second predetermined amplitude with each complete rotation of said first cam.
 9. A lens grinding machine as recited in claim 1 wherein said means for moving said block in said second orbit further comprise a machine frame, said first drive shaft supported in said frame, means for rotating said first drive shaft about said first axis of rotation, an oscillating platform eccentrically mounted on said first drive shaft being adapted to move in a circular orbit on rotation of said first drive shaft, means to support said oscillating platform for oscillating motion in said machine frame, a pivot shaft rigidly mounted in said oscillating platform and means connecting said pivot shaft to said lens carrying block.
 10. A lens grinding machine as recited in claim 9 wherein said means for maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relation with respect to said lap surface during the simultaneous orbiting of said lap and said block comprise an arm mounted for pivotal movement with respect to said oscillating platform along a second axis, a pin holder shaft mounted for pivotal movement relative to said arm about a third axis perpendicular to and spaced from said second axis, a block holder arm mounted on said pin holder shaft, a pin holder integral with said block holder arm, a pair of block holder pins extending downwardly from said pin holder, said lens carrying block being adapted to receive said pair of block holder pins and to permit pivotal movement of said block with respect to said pins about an axis parallel to said second axis, and means for exerting a predetermined downward pressure on said arm.
 11. A lens grinding machine as recited in claim 3 wherein the major axis of said first orbit is at least twice the minor axis of said first orbit.
 12. A lens grinding machine as described in claim 4 further comprising a second cam lever shaft mounted in said tilt frame, a second lap support mounted on said second cam lever shaft, said second cam lever shaft being mounted for pivotal movement relative to said tilt frame about a fourth axis parallel to said third axis, said means for pivotally moving said first cam lever shaft about said third axis further comprising means to simultaneously pivotally move said second cam lever shaft about said fourth axis through said second predetermined amplitude.
 13. A lens grinding machine as recited in claim 12 wherein said means for pivotally moving said first and second cam lever shafts about said third and fourth axes, respectively, further comprise a second cam, said second cam being eccentrically mounted on said second drive shaft, a first cam lever mounted on said first cam lever shaft and being adapted to rotate with said first cam lever shaft, a first cam follower mounted on said first cam lever, a second cam lever mounted on said second cam lever shaft and being adapted to rotate with said second cam lever shaft, a second cam follower mounted on said second cam lever, means for maintaining said first and second cam followers in contact with said second cam, whereby on rotation of said second drive shaft each of said first and second cam lever shafts is pivotally moved about its corresponding third and fourth axes, respectively, through said second predetermined amplitude with each complete rotation of said first cam.
 14. A lens grinding machine as recited in claim 13 wherein said means for maintaining said first and second cam followers in contact with said second cam comprise a tension spring connecting said cam levers.
 15. A lens grinding machine as recited in claim 14 further comprising means to adjust the tension in said spring.
 16. A lens grinding machine as recited in claim 1 further comprising a second lens carrying block and wherein said means for moving said block in said second orbit simultaneously with the orbital movement of said lap further comprise means to simultaneously move said second block in a third orbit substantially identical to said second orbit.
 17. A lens grinding machine as recited in claim 16 further comprising a machine frame, said first drive shaft supported in said frame, means for rotating said first drive shaft about said first axis of rotation, an oscillating member eccentrically mounted on said first drive shaft being adapted to move in a fourth orbit substantially identical to said second and third orbits on rotation of said first drive shaft, means to support said oscillating member for oscillating motion in said machine frame, a pivot shaft rigidly mounted in said oscillating member, means connecting said pivot shaft to said lens carrying block, and independent means connecting said pivot shaft to said second lens carrying block.
 18. A lens grinding machine as recited in claim 9 wherein said means to support said oscillating member for oscillating motion in said machine frame comprise a pair of idler cranks mounted in said machine frame.
 19. A lens grinding machine as recited in claim 10 wherein said means for exerting a predetermined downward pressure on said arm comprise a cylinder and piston means mounted on said machine frame, a pressure pin integral with said piston means, a socket in said arm to receive said pressure pin, and means to supply fluid under pressure to said cylinder and piston means.
 20. A lens grinding machine as recited in claim 3 wherein said means for pivotally moving said tilt frame about said second axis comprise a second drive shaft, means mounted on said tilt frame for rotating said second drive shaft, a circular member eccentrically mounted on said second drive shaft and being adapted to rotate with said drive shaft, a block, said circular member being mounted for rotation with respect to said block, and hinge means connecting said block to said machine frame whereby on rotation of said second drive shaft said tilt frame is pivotally moved about said second axis through said first predetermined amplitude with each complete rotation of said second drive shaft.
 21. A lens grinding machine as recited in claim 20 wherein said means for pivotally moving said first cam lever shaft about said third axis comprise a first cam lever mounted on said first cam lever shaft and being adapted to rotate with said first cam lever shaft, a cam eccentrically mounted on said second drive shaft and being adapted to rotate with said second drive shaft, and a cam follower mounted on said first cam lever and adapted to rotate against said cam, whereby on rotation of said second drive shaft said first cam lever shaft is pivotally moved about said third axis through said second predetermined amplitude with each complete rotation of said second drive shaft.
 22. The method of forming a compound curvature on a lens surface comprising moving a lap having a compound curvature on the surface thereof in a first orbit which in a reference plane describes substantially an ellipse, simultaneously moving a lens carrying block in a second orbit which in said reference plane describes substantially a circle, said reference plane being a plane normal to the axis of rotation of said circular orbit, and maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relation with respect to said lap surface during the said orbiting of said lap and said block.
 23. The method as recited in claim 22 wherein said lap is moved in said first orbit at between About 115 and 125 orbits per minute and said block is moved in said second orbit at between about 850 and 900 orbits per minute.
 24. The method as recited in claim 22 wherein the major axis of said second orbit is at least twice the length of the minor axis of said second orbit.
 25. A lens grinding machine for forming a compound curvature on a lens surface comprising a lap having a compound curvature on the surface thereof, means for moving said lap in a first orbit, a lens carrying block, means for moving said block, simultaneously with the orbital movement of said lap, in a second orbit, wherein one of said lap and said block moves in an orbit which in a reference plane describes substantially a circle and the other of said lap and said block moves in an orbit which in said reference plane describes substantially an ellipse, and means for maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relationship with respect to said lap surface during the simultaneous orbiting of said lap and said block.
 26. The method of forming a compound curvature on a lens surface comprising moving a lap having a compound curvature on the surface thereof in a first orbit, simultaneously moving a lens carrying block in a second orbit, wherein one of said lap and said block moves in an orbit which in a reference plane describes substantially an ellipse, the other of said lap and said block moves in an orbit which in said reference plane describes substantially a circle, said reference plane being a plane normal to the axis of rotation of said circular orbit, and maintaining said lens surface in close contact with said lap surface and in a predetermined aligned relationship with respect to said lap surface during said orbiting of said lap and said block. 